Wrong setup or bug - particle sim changes lightning

I wanted the particle sim to spawn some stuff around a tree for a christmas video. But the lightning changes as soon as particles are spawned.

I managed to isolate it into a single comp (I know the setup does not look nice, it is just for demonstration). After 5 seconds the partice sim should spawn squeres around the tree for a few seconds. As soon as the first particle is spawned the lighting of the sceene changes completely. Do I miss something?

The behaviour is different if layer is set to 3D plane which is not intended since the camera is supposed to move around.